Help sending ASCII via socket COMM

I am very new to programming PLCs, and one of the first tasks I received was to create a program that creates a socket connection between my PLC and another company's computer.

By using Allen Bradley's socket manual, I was able to do so without issues. I can send messages to the guy's computer with no problems!

However, he is requesting I send specific messages in a specific order with ascii codes.

HERE is an example of what kind of message to send:


<STX>00001|KEEPALIVE<ETX>

Start of Text - # of message – Field Separator – Message Data – End of Text


I know CONCAT, and can combine all the strings etc, but how to I actually send the "STX and "ETX" in raw ascii code?

My PLC is a compactLogix 5380, and I use PuTTY to test everything.

Here is a link with ASCII control codes:

https://ascii.cl/control-characters.htm

Hopefully this will help you with your issue.

chavn said:

Here is a link with ASCII control codes:

https://ascii.cl/control-characters.htm

Hopefully this will help you with your issue.

Click to expand...

Thanks for the reply. I have those codes on hand but how do I actually use them to send in a message?

Right now I have it set up to send a message in the form of a SINT[480].

How do I physically get the "start of text" and "end of text" in that?

shallels said:

Thanks for the reply. I have those codes on hand but how do I actually use them to send in a message?

Right now I have it set up to send a message in the form of a SINT[480].

How do I physically get the "start of text" and "end of text" in that?

Click to expand...

I once had a task close to this, and did the following:

Make sure the first SINT in the array has the value of STX and the last value of your message to send has the value of ETX.

So your first SINT would be STX and your last would be ETX

(Caveat - I am not an Allen Bradely/Rockwell user)

I googled non-printable ASCII characters for Rockwell and came up with this link http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1756-pm013_-en-p.pdf which is the "Logix 5000 Controllers ASCII Strings" manual which I believe should be relevant in general for your controller.

On page 18 of that document it shows an example that has in it:

The $14 counts as one character. The hex code for the Ctrl-T character.

Click to expand...

I think this is the sort of thing that you are looking for.

To enter special characters you can use "$" prefix.
in String editor you can use $10 and $11 to represent STX and ETX

You can also use MOV instruction to populate specific charcters for example
MOV 16#10 MYSTRING.DATA[0]
MOV 16#11 MYSTRING.DATA[xx]